Group sex most commonly takes place in a private sex party or semi-public swinger gathering, but may also take place at massage parlors or brothels or, in some jurisdictions, at purpose-built locations such as sex clubs. In places where non-monogamous sex is taboo or illegal, group sex may take place in private or clandestine locations including homes, hotel rooms, or private clubs.

In principle, any sexual behavior performed by more than two people can be referred to as group sex, but various terms are used to describe particular acts or combinations of people. Many swingers argue that non-swingers have conflated the terms because of lack of understanding and that there are distinct differences among the terms with specific meanings as to number, intent, sexual orientation, and familiarity of the persons involved.

When a person is entered or penetrated in the vagina and/or anus by two people at the same time. This usually is when one enters the anus while another enters the vagina, although it does also refer to two simultaneous penetrations in the same orifice.

Fantasies of group sex are extremely common among both men and women. In major studies, between 54 and 88% of people fantasize about watching others have sex, between 40 and 42% fantasize about being watched by others, and between 39 and 72% fantasize about bondage.[2] Many forms of sexual behavior were reported by Kinsey's subjects, but the official Kinsey Reports web site does not mention threesomes or group sex in the summary of Kinsey's findings.

A sex party is a gathering at which sexual activity takes place. Sex parties may be organized to enable people to engage in casual sexual activity or for swinging couples or people interested in group sex to meet, but any gathering where sexual activity is anticipated can be called a sex party.

Sex parties, under various names, have been a common focus of moral panics fed by media reports claiming that such parties are prevalent, or growing in prevalence, especially among teenagers.[3]

A swinger party or partner-swapping party is a gathering at which individuals or couples in a committed relationship can engage in sexual activities with others as a recreational or social activity.[4] Swinging can take place in various contexts, ranging from a spontaneous sexual activity at an informal social gathering of friends to a regular social gathering in a sex club (or swinger club) or residence.[5]

Swinger parties may involve various group sex activities. Partners can engage in penetrative sex, known as "full swap", or choose to "soft swap" in which they engage only in non-penetrative sex. New swinging couples often choose a soft swap before they are comfortable with a full swap, although many couples stay soft swap for personal reasons.[6] "Soft swinging" is when a couple engages in sexual activities with only each other while other couples perform sex acts in the immediate vicinity.[7] Technically this is a form of exhibitionism rather than "group sex" per se.

A key party is a form of swinger party, in which male partners place their car or house keys into a common bowl or bag on arriving. At the end of the evening the female partners randomly select keys from the bowl and leave with that key's owner.[8]

A rainbow party is an urban legend spread from the early 2000s. At these events, allegedly increasingly popular among adolescents, females wearing various shades of lipstick take turns fellating males in sequence, leaving multiple colours on their penises.[9] Rainbow parties were covered on The Oprah Winfrey Show in 2003, and became the subject of a juvenile novel called Rainbow Party.[9] On May 27, 2010 the television program The Doctors discussed the topic with dozens of teens, parents, and professionals. However, sex researchers and adolescent health care professionals have found no evidence for the existence of rainbow parties, and as such attribute the spread of the stories to a moral panic.[9]

A system of initialisms has evolved to describe the variety of group sex arrangements. These codes can appear in erotic literature and film descriptions, member profiles in online communities, and personal ads. These codes consist of arrangements of the letters M (for male) and F (for female). Adjacent letters are sometimes used to signify sexual contact between the participants represented by those letters, though this does not necessarily mean there is no contact between the other participants. For example, MMF would signify a ménage à trois of two men and one woman in which the center male has sexual contact with the other male and the female, and in which it is not specified whether there is contact between the female and the other male. MFMF (situation pictured in photo to right), on the other hand, implies no same-sex contact.

Variations on this system exist that use case to convey more information. Within the BDSM and D/s subcultures, upper and lower case letters can signify dominant (or top) and submissive (or bottom).

A daisy chain refers to sexual relations among three or more people, with each person both performing and receiving oral sex simultaneously.[11] Some sources consider only groups of five or more people to be a daisy chain.[12]

Self-evidently, for a closed daisy chain to be entirely heterosexual there must be an equal number of males and females, making the number of participants even. An odd number of participants would result in two people having to connect "both ways" to complete the chain.[13][14]

Thus, in an “erotic foursome or partie-carrée”, “two couples ... form a chain or Maltese cross carefully alternating man and woman”.[15]

"The matter of ... erotic or spintrian chains ("daisy-chains")",[16] i.e, "of "spintries" or erotic human chains, ... has been taken to ... permutational development in the appendix of postures to the well-known Manual of Classical Erotology (1824) of the Fichtean philosopher, Friedrich Karl Forberg, and in a Swedish work, Ju fler vi är tillsammans (“The More the Merrier”), by a schoolteacher, Ragnar Aaslund, published in 1966 and intended frankly as a manual of group-sex."[17]

Bukkake is a group sex practice where multiple men ejaculate onto the face or body of a female or male subject. At the end of the process, the subject may drink the semen, called gokkun. Its first filming is credited to adult filmmaker Kazuhiko Matsumoto in 1998. Bukkake originally became a pornography trend because of the mandatory porn mosaic in Japan. Since the directors could not show penetration they had to figure out new, visually appealing ways to approach sex acts that would satisfy the audience without violating Japanese law.

As with all sexual activity, the relative risks of group sex depend on the specific activities engaged in, although having a large number of sexual partners increases one's risk of exposure to sexually transmitted infections (STIs).

From the mid-1980s there was lobbying against gay bathhouses blaming them for the spread of STIs, in particular HIV, and this forced their closure in some jurisdictions, particularly in the United States.[18][19] Sociologist Stephen O. Murray, writes that, "there was never any evidence presented that going to bathhouses was a risk-factor for contracting AIDS."[20] In other countries, fears about the spread of STIs have prompted the closing of bathhouses—with their private rooms—in favour of sex clubs, in which all sexual activity takes place in the open, and can be observed by monitors whose job it is to enforce safer sex practices.[21]

Proponents point out that venues where group sex takes place often provide condoms, dental dams, latex gloves, lubricants and other items for safer sex. Bathhouses in particular are a major source of safer sex information—they provide pamphlets and post safer sex posters prominently (often on the walls of each room as well as in the common areas), provide free condoms and lubricants, and often require patrons to affirm that they will only have safer sex on the premises.[22][23][24][25]

Sensational media reports about the prevalence of sex parties, especially among young people, appear with some regularity. In the early 1950s, for example, it was alleged that teenage girls, mainly throughout the Southern and MidwesternUnited States were forming "non-virgin clubs", in which they organized and held sex orgies with reports of couples being paired off by drawing numbers from a hat. These claims were investigated and debunked.[27][28][29][30]

Several stories of this type arose in the US in 2003. In New York, rumors began that teens had been taking days off from school to attend "hooky parties" while their parents were at work. One school even suspended a group of girls for allegedly skipping school to attend such a party. They were refused the right to return to school until each had submitted to a medical examination for sexually transmitted diseases and pregnancy and school officials were allowed to examine the results. The New York Civil Liberties Union filed a federal lawsuit against the school[31] on behalf of the girls and won a settlement which included monetary damages and a change in the school district's policy.[32]

Similar stories concerning teenagers using gel bracelets as coupons or signals for sex also arose at the time, with a similar lack of corroborating evidence.[33]

^Gross, Jane (October 14, 1985). "Bathhouses reflect AIDS concerns". The New York Times. Retrieved 26 December 2006. At the St. Marks Baths, for the price of a locker or a room, patrons now get a free condom, enclosed in a package that bears the legend the contents of this envelope could save your life.

Weill, Sabrina (2006). The Real Truth About Teens and Sex: From Hooking Up to Friends with Benefits – What Teens Are Thinking, Doing, and Talking About, and How to Help Them Make Smart Choices. New York: Perigee. ISBN978-0-399-53280-1.